Along with an increase in the population of old people, there have been increasing demands for a small-size traveling mechanism for personal use, and its typical example includes a small-size traveling mechanism with wheels, such as an electric motor cart and an electric motor chair. However, within a range where such a small-size traveling mechanism is allowed to run, various step differences exist, thereby forming obstacles against its movements. In a case of a normal wheel-type small-size traveling mechanism, since the positions of the wheels relative to a seat are set to be virtually constant, the height of a step difference that the mechanism can cross over is dependent on a wheel base that corresponds to the wheel diameter and the gap between the front wheel and the rear wheel, and it becomes difficult to cross over such a step difference exceeding 10 cm.
Here, as the small-size traveling mechanism that is suitable for this step difference, a leg-type small traveling mechanism has been proposed (for example, see Non-Patent Document 1). By adopting a leg-type structure, it becomes possible to be applied to a big step difference with which the wheel-type small-size traveling mechanism fails to deal.
However, since the leg-type small-size traveling mechanism is inferior to the wheel-type small-size traveling mechanism in its mobility on plane places other than a step difference, a leg-wheeled small-size traveling mechanism, made by combining the two mechanisms with each other, has been proposed (for example, see Patent Documents 1 and 2).
Patent Document 1: Japanese Unexamined Patent Publication No. 11-128278
Patent Document 2: Japanese Unexamined Patent Publication No. 2006-055972
Non-Patent Document 1: Preprints 1G24 for the 23rd Annual Conference of the Robotics Society of Japan